The aim of this study was to investigate whether addition of porcine epididymal fluid (pEF) into culture medium during in vitro maturation influences the nuclear maturation of porcine germinal vesicle (GV) oocytes. Porcine cumulus-oocyte complexes (COCs) from follicles were cultured in tissue culture medium 199 (TCM 199) containing pEF. After 48 hr of culture, oocytes were examined for evidence of GV breakdown, metaphase I, anaphase-telophase I, and metaphase II. The proportion of oocytes reaching at metaphase II (M II) stage was significantly (p<0.05) increased in oocytes cultured in the media supplemented with 10% pEF during in vitro maturation than in those without pEF regardless of cumulus presence or absence (54.6% vs 22.5%，51.7% vs 24.2%). The supplementation of pEF during maturation of oocyte enhanced oocytes maturation in a dose-dependent manner in vitro. Also significant differences (p<0.05) in the percentage of MII oocytes were observed according to exposure period in pEF. Present study suggests that pEF contains a enhancing component(s) for nuclear maturation of porcine immature oocytes in vitro.